Abstract

This tutorial will describe how to create your own plugin ("add comics") for the
comic plasmoid. You need at least KDE 4.2 to be able to create plugins.

In general you can create plugins in any language supported by Kross, though
this tutorial will focus on QtScript (JavaScript, ECMAScript), as this is
supported by any KDE installation out of the box.

You do not have to be experienced in QtScript to be able to write comic plugins, often adapting existing plugins is enough. But in any case http://www.w3schools.com/JS/default.asp is a good reference and tutorial for javascript.

Keep in mind that not all supported features are discussed here at the moment.

Type of comics

There are three different types of comics that are supported by the comic
dataengine.

date

number

string

That is the way the comics are identified, like "garfield:2000-01-01" or
"xkcd:100", string can be anything.

Sometimes the website your comic is published on neither have an easy way to get a date or a number to a comic strip or that would not help to access the strip, in that case you should use string.

The idea of this is that the type should be enough to get the comic e.g.
"xkcd:100". The first part tells what plugin should be loaded and the last part tells your plugin what comic strip should be loaded. Your plugin won't get more information from the dataengine on the request than that.

Package Structure

The comic plugins are provided as packages that can be uploaded to
www.kde-files.org and easily downloaded from that place directly from the
applet.

First create a folder you want to work in. You need a structure like the
following:

./metadata.desktop

./icon.png

./contents/code/main.es

Later you need to zip the files to a ".comic"-package, you can do that with e.g.

zip -r my_comic.comic contents/code/main.es metadata.desktop icon.png

where "my_comic" is the name of the comic you want to add.

The metadata.desktop file

X-KDE-Library=plasma_comic_krossprovider
X-KDE-PluginInfo-Author=Your Name
X-KDE-PluginInfo-Email=Your email-adress
X-KDE-PluginInfo-Name=my_comic
X-KDE-PluginInfo-Version=0.1
X-KDE-PluginInfo-Website=http://plasma.kde.org/
X-KDE-PluginInfo-License=GPLv2
X-KDE-PluginInfo-EnabledByDefault=true
X-KDE-PlasmaComicProvider-SuffixType=Date
In the "Name" and "Comment" section add the name of the comic you want to add.
It will show up in the comic list (that is not the "Get New Comics..."-dialog)
under that name. You could also translate the name of the comic to different
languages e.g.

Name[de]=Mein Comic
Comment[de]=Mein Comic

You only need "Icon" if you have an icon for your comic -- like a favicon. In this example, the file is called "icon.png".

X-KDE-PluginInfo-Name is very important, as that is the name of your plugin. The comic dataengine will use this name to identify what comic plugin should be loaded. You also need this name if you test your plugin with the plasmaengineexplorer. There is no white space allowed in the name.

X-KDE-PlasmaComicProvider-SuffixType is the type of the comic as discussed the section above ('date', 'number', or 'string').

The Code

In the first two sections I am discussing what functions and objects are
available, if you want you can skip these sections and use them only as reference if needed.

If the download was successful the dataengine will call pageRetrieved.

pageRetrieved(id, data)

pageRetrieved is only called if you asked the dataengine to download something for you.

What data is depends on the id.
If the id is comic.Image then data is the image, making any changes to data will change the image being displayed by the comic plugin. In all other cases data is the downloaded data in a byte stream converted to unicode -- in some cases not see comic.textCodec at [Available Objects] -- while id defines what kind of download it was. You can convert the byte stream to a String if needed:
var dataString = data.toString();
var begin = dataString.indexOf( "test" ); //would not work without the conversion

Here you could search in the data for the URL to the comic strip, the title of the comic, the comic's author, the identifier for the next comic, etc.
So you only need to implement that function if you want to find something in a webpage or if you want to modify the image.

comic.combine(image, position)

As the comic dataengine can not handle multiple pictures itself you have to combine several pictures to one occasionally.

For this you can use comic.combine(image, position). image needs to be an image, while position can be one of the following:

comic.Left

comic.Top # that is the default

comic.Right

comic.Bottom

image will be combined with the last downloaded image -- comic.pageRequest(url, comic.Image). The position defines, where image will be placed. That way you can combine multiple images.

The following code is taken from the Deo Ignito comic plugin. I removed parts that are not nescessary for explaining this function, added some comments and pseudo code.

var firstImage = 0;
//the variable we will temporaly store the combined images in,
//so this is the image that all other pictures will be combined with
//e.g. 4 different pictures 1,2,3,4
//1. 4
//2. 3 and 4 --> 34
//3. 2 and 34 --> 234
//4. 1 and 234 --> 1234
//as you might have guessed, we are using comic.Bottom here, as that
//works good with Array::pop()

var urlArray = new Array();
//the array that will store the urls to the pictures

if (urlArray.length > 0) {
//asking for another image-download will overwrite the previous
//image, that is why we store the current image(-combination)
//before requesting another image
firstImage = comic.image();

comic.requestPage(urlArray.pop(), comic.Image);
}
}

}

Another comic plugin that currently uses this feature is Shit Happens!, though in this case an image provided by the comic-package is combined with the comics.

date-functions

Here I'm showing only two examples of the date-object and its member functions. If you want more information look at the sourcecode of comicproviderwrapper.h, comicproviderwrapper.cpp and look at the Qt-documentation as this object was designed to work similar to QDate. In some cases there might be differences though!

comic.requestRedirectedUrl(url, id, metadata)

Introduced with API version 4450.

Sometimes you only have a relative url, e.g. next would be current url + "/?relid=X&go=+1". This function helps you to get the real url this relative url points to. This is useful for cases where you don't know the next or previous identifier, while this information is embded in the "real" url.

Ask the dataengine to retrieve the real (redirected) url for url. id specifies of what type the download is. There are some predefined ids:

comic.PreviousUrl

comic.NextUrl

comic.CurrentUrl

comic.FirstUrl

comic.LastUrl

comic.UserUrl

Those are for convenience only, you could use any integer you want.

You can also add metdata though that is optionial. For more information on metadata see [1]

This method will always call redirected(id, url). If there was no redirection, then it will be called with the original url.

redirected(id, url)

Introduced with API version 4450.

Only called when you called comic.requestRedirectedUrl.
Will either contain a redirected url or the original url.

Available objects

In this section the available objects that you can assign something are listed and described.
Only comic.identifier and some other identifiers in special
cases -- as discussed below -- have something assigned to them initially.

comic.comicAuthor = "Randall Munroe"; //the author or authors of the comic strip
comic.websiteUrl = "http://xkcd.com/42/"; //the address to the page where the strip is
comic.shopUrl = "http://store.xkcd.com/"; //if there is a shop for the comic
comic.title = "Geico"; //the title of the comic strip, can be also the chapter etc.
comic.additionalText = "David did this"; //additional text, that will be shown as tooltip in the comic applet.
comic.textCodec = "Windows-1251"; //Only set the codec of the web content if it is not automatically recognized! So test first if it works without setting it.
comic.isLeftToRight = false; //true is the default, only set if the comic is not LTR (introduced with 4.3)
comic.isTopToBottom = false; //true is the default, only set if the comic is not from TopToBottom (introduced with 4.3)

comic.apiVersion

Introduced with API version 4450.

Will return the version of the api as an integer. That is the earliest KDE SC release that contains all features of the currently running api. E.g. if the API of KDE SC 4.5.0 is the same as of 4.4.5 then the api version would be 4450 for both.

The number is done the follwing way 'series of KDE' + 'major version' + 'minor version' + 'placeholder'. So 4.4.5 would become 4450, the last digit -- the place-holder -- is there if the need arises to modify the api inbetween minor releases, e.g. security fixes.

You can call this function also if your API version was older than 4450, in that case undefined would be returned, comparing it to an integer would always return false.

if (comic.apiVersion >= 4450) {

comic.requestRedirectedUrl(url, id);

} else {

//... do something

}

Identifier

There are six "identifier" objects, that react differently depending on the type of the comic.

comic.identifier //the identifier of the recent comic strip
comic.firstIdentifier //the first comic strip e.g. number 1
comic.lastIdentifier //the last (most recent) comic strip e.g. number 42
comic.previousIdentifier //the previous identifier of the current strip e.g. number 40
comic.nextIdentifier //the next identifier of the current strip e.g. 41
comic.identifierSpecified //if the caller of the dataEngine specified an (bool) identifier

comic.identifier is the identifier the dataengine is being asked for, so it is already set, though you can assign something different to it if needed.

If comic.identifierSpecified is false you should download the most recent comic strip. Note: This is introduced in KDE 4.2.1 and KDE 4.3, it fixes some problems.

For some types what you assigned to comic.identifier, comic.lastIdentifier, or comic.firstIdentifier will be checked and comic.identifier will be modified accordingly.

If there is a nextIdentifier then the dataengine will cache the comic strip, it does not need to be downloaded again in the future.

date

comic.identifier will always be an actual date that exists, if no exact date has been specified by the caller of the dataengine it will be today.

If you are assigning something to comic.lastIdentifier, then comic.identifier will be reassigned that day automatically, but only if comic.identifier was a day after comic.lastIdentifier, or if comic.identifierSpecified is false e.g.:

comic.lastIdentifier = date.fromString("2009-02-01");
print(comic.identifier); //still 2009-01-10
In any case comic.identifier will be in the specified range you defined.

comic.previousIdentifier and comic.nextIdentifier will also be checked (KDE 4.2.2+):

if comic.identifier is comic.firstIdentifier there won't be a comic.previousIdentifier

if comic.identifier is comic.lastIdentifier there won't be a comic.nextIdentifier

If you do not set both (!) comic.previousIdentifier and comic.nextIdentifier
then they will be set automatically according to this rules:

comic.previousIdentifier = comic.identifier - 1 day;

comic.previousIdentifier never will be a day before comic.firstIdentifier

comic.nextIdentifier = comic.identifier + 1 day;

comic.nextIdentifier never will be a day after comic.lastIdentifier

You should set the identifiers yourself if the comic is _not_ end-to-end e.g.
2009-01-12, 2009-01-14, 2009-02-01, ... If you are not sure also set the identifiers yourself.

number

comic.identifier will either be a specific number, or if no number has been
specified by the caller of the dataengine it will be "0".

Using comic.identifierSpecified (recommended!) you can have a comic that is identified by the number "0", if you don't use comic.identifierSpecified you have to shift everything see Digital Purgatory as an example.

print(comic.identifierSpecified); //suppose that it is false
comic.lastIdentifier = 20;
print(comic.identifier); //would be 20 now

In any case comic.identifier will be in the specified range.

comic.previousIdentifier and comic.nextIdentifier will also be checked (KDE 4.2.2+):

if comic.identifier is comic.firstIdentifier there won't be a comic.previousIdentifier

if comic.identifier is comic.lastIdentifier there won't be a comic.nextIdentifier

If you do not set both (!) comic.previousIdentifier and comic.nextIdentifier
then they will be set automatically according to this rules:

comic.previousIdentifier = comic.identifier - 1;

comic.previousIdentifier never will be smaller than comic.firstIdentifier

comic.nextIdentifier = comic.identifier + 1;

comic.nextIdentifier never will be larger than comic.lastIdentifier

You should set the identifiers yourself if the comic is _not_ end-to-end e.g.
1,4,5,9 ... If you are not sure also set the identifiers yourself.

string

Here you have to set nearly everything you want to use yourself, only one thing is set
automatically.
comic.identifier will either be a specific string, or if no string has been
specified by the caller of the dataengine it will be an empty string (length = 0).

Note: 4.2.1+
print(comic.identifierSpecified); //suppose that it is false
comic.lastIdentifier = "muahaha";
print(comic.identifier); //would be "muahaha" now

comic.image()

Accesses the image object.

Following is an example that works with apiVersion 4600. It sets the last frame of an animation as used image. In fact before this can work data has to be set e.g. via comic.requestPage(url, comic.Image).

var img = comic.image();
if (comic.apiVersion >= 4600) {

var count = img.imageCount();//The number of frames if it is an anmiation, otherwise 0 or -1 if there was an error
if (count >= 0) {
var temp;
for (i = 0; i < count; i++) {
temp = img.read();//reads the next frame and stores it in temp
}
img.image = temp;//sets the last frame as image
}

}

Examples

In this section there are some working examples -- for every type of comic one -- that should give you more insight of what comic plugins look like. You can look at other examples by downloading comic plugins either directly from kde-files.org or by installing further comics by using the "Get New Comics..."-dialog, then you find the installed comics and their code at

~./kde4/share/apps/plasma/comics/ # maybe ".kde" in your case

Note: These examples are based on 4.2, for 4.2.1+ some would need modification according as described in the previous section.

date

This example shows the implementation of the comic plugin for Jesus and Mo.

* Copyright (C) 2009 Matthias Fuchs <mat69 AT YOU KNOW DELETE THAT gmx.net> *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
* This program is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with this program; if not, write to the *
* Free Software Foundation, Inc., *
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA . *
***************************************************************************/

number

This example shows the implementation of the comic plugin for xkcd
<code javascript>
/*

* Copyright (C) 2007 Tobias Koenig <tokoe AT YOU KNOW DELETE THAT kde.org>
* Copyright (C) 2009 Matthias Fuchs <mat69 AT YOU KNOW DELETE THAT gmx.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Library General Public License version 2 as
* published by the Free Software Foundation
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details
*
* You should have received a copy of the GNU Library General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/

string

* Copyright (C) 2008 Matthias Fuchs <mat69 AT YOU KNOW DELETE THAT gmx.net> *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
* This program is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with this program; if not, write to the *
* Free Software Foundation, Inc., *
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA . *
***************************************************************************/

//cehck if the comic.identifier is empty, there are other ways as well like checking its length
if (comic.identifier != new String()) {
comic.websiteUrl += comic.identifier;
comic.requestPage(comic.websiteUrl, comic.Page);
} else {
comic.requestPage(comic.websiteUrl + comic.firstIdentifier, comic.User);
}

as you do not have to have reinstall the plugin if you change something. If you
are finished and changed something on the main.es file simply store the main.es
in your original folder and use the zip-command mentioned above to update the
package.

To test your plugin type

plasmoidviewer comic

and choose your plugin. That way you will see debug-output.
Alternatively you could use the plasmaengineexplorer

plasmaengineexplorer

there choose comic and type in your comic identifier e.g.

garfield:

or

garfield:2000-01-01

All the comic strips that have a next identifier will be cached at

~/.kde4/share/apps/plasma_engine_comic/ # maybe ".kde" in your case

so if you change the applet it might be good to clean the cache before further testing by

I add "****" in the print to find the output more easily.
Sometimes when I do not find the error at first sight I add a lot print statements like in the example above to find the error (e.g. written something wrong, forgot something etc.).

In case all that does not work and pageRetrieved is still called you could use
<code javascript>
print(data);
</code>
so that you can check if the data is correct and if it is what you expected.

Publishing on kde-files.org

First you should deinstall the plugin by

plasmapkg -t comic -r my_comic

and then you need an account on www.kde-files.org. If you have done all that
go to the "Plasma Comics" section and contribute your plugin. It will show up
in the "Get New Comics..."-Dialog after a while.